Ethernet transport is an emerging opportunity for telecommunication carriers. This service provides point-to-point Ethernet connectivity and offers different types of services with many combinations of quality objectives, such as loss, delay and bandwidth. This opportunity is created by the access network quickly becoming a bottleneck as new applications demand more and more bandwidth. Traditional access equipment using SDH and xDSL do not offer the speeds required to transport all the new multimedia applications including, for example, triple-play, Fixed-Mobile-Convergence (FMC) and IP multimedia sub-systems (IMS).
To address these access challenges, telecommunications carriers have selected Ethernet. They need to be able to deploy rapidly a wide ranging variety of services and applications without the need to constantly modify the network infrastructure. Enterprises have long used Ethernet as the technology to support a variety of applications requiring different qualities of service (QoS) from the network. Carriers are leveraging this flexibility and are standardizing on this technology to offer data access services.
Using this service definition, existing network elements which offer network access using Ethernet technology are not designed to make maximum use of the legacy network links existing at the edge of the carrier networks. Many access technologies such as DSL or WiMAX are prone to errors which affect the link speed. The network devices are unable to react to these errors to ensure that the service level agreements are met. The following inventions are focused on addressing these challenges.
Flow Control
When a telecommunications provider offers an Ethernet transport service, a service level agreement is entered with the customer which defines the parameters of the network connection. As part of this agreement, bandwidth objectives are defined in terms of Committed Information Rate (CIR) and Excess Information Rate (EIR). The CIR guarantees bandwidth to a connection while the EIR allows the connection to send at higher bandwidth when available.
The telecommunications provider verifies the traffic from each connection for conformance at the access by using a traffic admission mechanism such as policing or traffic shaping. The policing function can take action on the non-conforming packets such as lowering the priority or discarding the packets. Policing is necessary because the service provider can not rely on an end-point not under the control of the network provider to behave according to the traffic descriptor. In case of mis-behavior, the performance of the whole network can be affected. Policing does not take into account the reality of the application traffic flow and the dynamic modification encountered by a traffic flow when it is moving through the network. As packets get multiplexed and demultiplexed to and from network links, their traffic characterization is greatly modified. Another issue with policing and static characterization is that it is extremely difficult to set these traffic descriptors (i.e., CIR, EIR and burst tolerance) to match a given application requirement. The needs of the application change with time in a very dynamic and unpredictable way. Traffic shaping, in turn, buffers the incoming traffic and transmits it into the network according to the contracted rate.
To implement the Ethernet transport service in a provider's network, sufficient bandwidth is allocated assuming the connections fully use the committed bandwidth, even though that is not always the case, leading to inefficiencies. In case of excess low priority traffic, the network generally over-provisions the network in order to ensure that sufficient traffic gets through such that the application performance does not deteriorate.
Another inefficiency currently encountered in Ethernet networks is that traffic that has traveled through many nodes and has almost reached destination is treated the same as traffic just entering the network which has not consumed any resources. Current Ethernet network implementations handle congestion locally where it occurs, by discarding overflow packets. This wastes bandwidth in the network in two ways:
1. bandwidth capacity is wasted as a result of retransmission of packets by higher layer protocols (e.g., TCP)
2. Packets are lost throughout the network, wasting precious upstream bandwidth which could be used by other connections generating more revenues for the carriers.
The Ethernet protocol includes a flow control mechanism referred to as Ethernet Pause. The problem with Ethernet Pause flow control is it totally shuts off the transmission of the port rather than shaping and backing off traffic that it could handle. It is currently acceptable to do this at the edge of the network, but for a network link it would cause too much transmission loss, and overall throughput would suffer more than causing a retransmission due to dropping packets.
There is a need to define a flow control mechanism for Ethernet that alleviates the need for local handling of congestion and allows intelligent optimized throttling of source traffic. Instead of requiring that applications comply with static traffic descriptors, it would be desirable to use real time feedback such that the applications can adapt their packet transmission to match the network state, allowing for a minimum throughput to guarantee the minimum requirement for the application. Some applications implicitly derive network status using jitter buffers, for example, but all other applications have to conform to a static set of traffic descriptors which do not meet their dynamic requirements.
Flexible Shaper to Reduce Delay or Loss
A traffic admission mechanism can be implemented using a policing function or a traffic shaper. Traffic shaping has a number of benefits from both the application and the network point of view. However, the shaper can delay the transmission of a packet into the network if the traffic sent by the application is very different from the configured traffic descriptors. It would be useful to make the shaper flexible to take into account the delays that a packet encounters so that different actions, such as lowering the priority or discarding, can be applied.
Network Migration
The key to the success of any new networking technology is to ensure seamless and cost-effective migration from existing legacy networks. Carriers cannot justify replacing complete networks to deploy new services, and thus the network overhaul has to be done gradually, ideally on a pay-as-you-grow basis.
Automatic Bandwidth Renegotiation
Once a customer has entered a service level agreement (“SLA”) with a carrier, this is fixed and can not easily be changed. To engineer the SLA, each customer application is required to characterize its traffic in terms of static traffic descriptors. However it is very difficult to make such characterizations without over-allocating bandwidth. For example, traffic patterns for videoconferencing, peer-to-peer communication, video streaming and multimedia sessions are very unpredictable and bursty in nature. These applications can be confined to a set of bandwidth parameters, but usually that is to the detriment of the application's performance or else it would trigger underutilization of the network. To add to this challenge, a customer's connections can carry traffic from multiple applications, and the aggregate behavior is impossible to predict. Also, the demand is dynamic since the number of new applications is growing rapidly, and their behavior is very difficult to characterize.
The demand for network resources also varies greatly depending on the time of day and the type of applications. There is a need for mechanisms to allow the applications to optimize their performance while maximizing the network usage.
Sub-Classes for Ethernet QoS
Carriers market only a limited set of Ethernet classes of service, generally three or four services covering the need for low latency/low jitter, low loss with guaranteed throughput and best effort for bursting. Given the number and varying types of applications and customers that a carrier handles, there is a need for further differentiation within a class of service to allow a carrier more flexibility in its tariff strategies.